1. Field
The embodiments described below relate generally to radiation treatment, and more particularly to imaging systems used in conjunction with such treatment.
2. Description
According to conventional radiation treatment, a beam of treatment radiation is directed toward a tumor located within a patient. The radiation beam delivers a predetermined dose of therapeutic radiation to the tumor according to an established treatment plan. The delivered radiation kills cells of the tumor by causing ionizations within the cells.
Treatment plans are therefore designed to maximize radiation delivered to a target while minimizing radiation delivered to healthy tissue. However, a treatment plan is designed assuming that relevant portions of a patient will be in a particular position relative to a treatment device during treatment. If the relevant portions are not positioned exactly as required by the treatment plan, the goals of maximizing target radiation and minimizing healthy tissue radiation may not be achieved. More specifically, errors in positioning the patient can cause the delivery of low radiation doses to tumors and high radiation doses to sensitive healthy tissue. The potential for misdelivery increases with increased positioning errors.
Due to the foregoing, treatment plans are designed under the assumption that positioning errors may occur that may result in misdelivery of radiation. Treatment plans compensate for this potential misdelivery by specifying lower doses or smaller beam shapes (e.g., beams that do not radiate edges of a tumor) than would be specified if misdelivery was not expected. Such compensation may decrease as margins of error in patient positioning decrease.
It would therefore be beneficial to provide a system and method that may increase the accuracy of patient positioning during radiation treatment. When used in conjunction with conventionally-designed treatments, more accurate positioning may reduce chances of harming healthy tissue. More accurate patient positioning may also allow the use of more aggressive treatments. Specifically, if a margin of error in patient positioning is known to be small, treatment may be designed to safely radiate a greater portion of a tumor with higher doses than in scenarios where the margin of error is larger.
Recent systems attempt to improve the accuracy of patient positioning by combining a device for emitting treatment radiation with a device for emitting radiation that is more suitable for creating images. In one example, a fixed device is provided to deliver imaging radiation perpendicularly to the direction of treatment radiation and toward a fixed imaging device. The perspective provided by a resulting image is not particularly useful in determining whether a tumor or body of interest is properly positioned with respect to the treatment head.